The principle nitrosourea anticancer agents (1,3-bis (2-chlorethyl)-1-nitroso-urea, BCNU; 1-(2-chlorethyl)-3-cyclohexyl-1-nitrosourea, CCNU; methyl-CCNU), used with some success in treating humans with cancer, cause delayed and cumulative bone marrow toxicity and secondary tumors in some patients. A property of these compounds which has been correlated with toxicity, antitumor activity, and carcinogensis is their ability to alkylate cellular DNA. In physiological conditions, nitrosureas decompose to alkyldiazohydroxides and chlorethyl carbonium ions that alkylate nucleic acids, and cause breaks in DNA. There are currently no simple methods available to detect and monitor damage induced by such compounds. One newer agent, chlorozoticin (CLZ) (chlorethyl nitrosourea attached to glucose), is more therapeutic, less myelosuppressive and produces 2-fold greater alkylation of RNA and DNA than BCNU or CCNU and no carbamoylation. Therefore, CLZ-modified calf thymus DNA has been injected intramuscularly and intradermally into rabbits to obtain antibodies for an ultrasensitive enzymatic radioimmunoassay (USERIA) to study macromolecular alterations in patients clinically exposed to these compounds and to experimentally study the mechanisms of their cellular effects.